ZYX Compilance

I agree - seems like the calcs aren't coming up with the right values or ones that make sense.  I've attached a link to a thread where GT Audio (I believe is the UK Rep for ZYX) says that ZYX recommends tonearms with effective mass of 12-20 gms - which puts it in the medium mass tonearm range.

https://pinkfishmedia.net/forum/threads/zyx-compliance-10hz-or-100hz.195170/

Thanks, quote as stated by GT Audio

EQ Compliance horizontal - 15×10-6cm/dyne
EQ Compliance vertical - 12×10-6cm/dyne

Recommended tonearm effective mass 12grams minimum/20grams maximum

With the TB or SB headshell added it will be:

+TB - recommended tonearm effective mass 9.5grams minimum/17.5grams maximum
+SB - recommended tonearm effective mass 7grams minimum/16.5grams maximum.

Therefore a tonearm with a medium effective mass is recommended for all of the above.

Could someone with a Zyx cartridge and a test record please send in their results. This seems like the only way to get a definitive answer.

I do have a Zyx cartridge & in my manual it simply says ’Compliance’ it does not state whether it is Dynamic or Static or what it is measured at either 10hz or 100hz, hence the reason for starting this topic.
If the compliance is how you have calculated at 25.5cu & using your ETA arm, according to the manual its effective mass is 22g with a 6.5g cartridge, I don’t know the weight of your 4D but my cartridge weight with SB is 7.9 so this would increase the mass with the ETA to 23.4g using the calculation in the article link by rdk777 we get an RF of 6.5 it is also stated in this article that the desired range is 9-11 so your combination is well outside the range.

My EPA-100 (not ETA) has been in use with ZYX Airy III without Silver Base, don’t forget that EPA tonearm has a very special counterweight mechanism to deal with cartridges with different compliance, you can read in Technics EPA-100 manual, this is unique option, no other tonearm will give you something like this. 

If we aim for an RF of 10 right in the middle of the desired range using your calculation of 25.5 compliance & my cartridge weight of 7.9g I would need an arm with effective mass of 21g. I would really appreciate your recommendations of an arm in this range.

Reed 3P "12 Cocobolo was my second arm when i upgraded from ZYX Airy III to ZYX Premium 4D Silver Base (7.9g) , the effective mass of my Reed tonearm was 18-19g (without cartridge). Reed is an excellent toneam for any cartridges, you can buy Reed in 9.5, 10 or 12 inch length and each wood has different mass, so you can buy what you need. Absolutely amazing tonearm with so many unique features. 

P.S. You don’t have to worry that much to keep your arm/cart resonance at 10Hz, this is theory, practically you will not hear the difference anyway, just try to stay in the range of 8Hz - 15Hz.

@chakster
The specs I was referring to were for the Technics EPA-100 it was just a typo.
If we take your Reed example with cart + arm = 25.9 (arm18g) with a compliance of 25.5 the Rf would be 6.19.
Could you do the equation and tell me if you get the same figure.
Surely if the compliance is 25.5 you would need a very low mass arm.

I can't because i no longer use ZYX since i discovered better  cartridges for my needs. 

But i told you that you can buy Reed with lower effective mass if you will look at shorter cocobolo armtube (10.5 or 9 inch) or just different wood for armtube, reed have many options.